Quox 1 homeobox protein is expressed in postmitotic sensory neurons of dorsal root ganglia.

The expression of vertebrate homeoproteins has been extensively studied in a variety of normal and cancerous tissues, but little is known on the role of vertebrate homeoproteins in the proliferation and differentiation of cells from these tissues. In the present study, we investigate the relationship between Quox 1 protein (a quail homeodomain containing protein) expression and the proliferation and differentiation of quail dorsal root ganglia (DRG) and neural crest cells. In vivo [3H]TdR labeling experiments demonstrate that the postmitotic sensory neuroblasts appear before the formation of the ganglion, and that more than half of sensory neuroblasts from DRG have already terminated their proliferation in embryos of 2 days of incubation (E2). All DRG neurons have completely ceased to proliferate from E6.5 onwards. By means of immunocytochemistry, we observe that Quox 1 protein is accumulated exclusively in all bipolar neurons in culture of DRG from E9-E11, and in all postmitotic sensory-like neuroblasts during in vitro cell differentiation of the neural crest. The Quox 1 immunoreactive neurons express simultaneously neurofilaments or substance P, and they are never labeled by anti-bromodeoxyuridine. These observations together with the morphology of Quox 1 positive cells, demonstrate that Quox 1 protein is expressed in the postmitotic sensory neurons of DRG. Our previous experiments have shown that between E4 and E6, the accumulation of Quox 1 protein increases in DRG in vivo, but decreases in the central nervous system in which cell proliferation decreases (Xue et al., (1993) Mech. Dev. 43, 149-158). Taken together, our results show that the accumulation of Quox 1 protein in DRG is tightly linked to the increase in the number of postmitotic neurons, whereas in the central nervous system the level of expression of Quox 1 seems concomitant with the extent of cell proliferation.